This invention relates to an aluminum alloy wire that is particularly suitable for use in conducting electricity, as well as to the manufacture thereof. The wire produced by the method of this invention has improved properties of yield strength and ultimate tensile strength which renders it particularly suitable for use in cable constructions requiring conductive elements capable of carrying large tensile loads.
Although the wire produced by the method of this invention will not normally have sufficient electrical conductivity and elongation characteristics such as to qualify it according to present standards for use in building wire, its high tensile strength properties, coupled with improved properties of fatigue resistance and creep resistance as compared with conventional aluminum alloys of similar electrical properties, renders it particularly suitable for use in overhead transmission cable and the like where the tensile strength is of primary significance and the electrical conductivity is of secondary concern.
In copending application Ser. No. 430,300, now U.S. Pat. No. 3,920,411 of which the instant application is a continuation-in-part, there is disclosed an aluminum alloy electrical conductor having a minimum conductivity of 58% IACS and consists essentially of from about 0.35 to about 4.0 weight percent cobalt, from about 0.1 to about 2.5 weight percent iron, the remainder being aluminum with associated trace elements, said aluminum alloy electrical conductor having the following properties when measured as a number 10 A.W.G. fully annealed wire:
Tensile Strength: 12,000-24,000 psi PA1 Elongation: 12 percent - 30 percent PA1 Yield Strength: 8,000 - 18,000 psi.
The conductor of the aforementioned application is formulated from an aluminum based alloy prepared by mixing cobalt, iron and optionally other alloying elements with aluminum in a furnace to obtain a melt having requisite percentages of elements. The aluminum content of the alloy could vary from about 93.50 percent to about 99.65 percent by weight. The optional alloying element or group of alloying elements could be present in a total concentration of up to 2.50 percent by weight, preferably from 0.1 percent to about 1.75 percent by weight.
After preparing the melt, the aluminum alloy was continuously cast into a continuous bar by a continuous casting machine and then, substantially immediately thereafter, hot-worked in a rolling mill to yield a continuous aluminum alloy rod.
As further described in the aforementioned copending application Ser. No. 430,300, now U.S. Pat. No. 3,920,411 a continuous casting machine serves as a means for solidifying the molten aluminum alloy metal to provide a cast bar that is conveyed in substantially the condition in which it solidified from the continuous casting machine to the rolling mill, which serves as a means for hot-forming the cast bar into rod or another hot-formed product in a manner which imparts substantial movement to the cast bar along a plurality of angularly disposed axes.
The continuous casting machine is of conventional casting wheel type having a casting wheel with a casting groove in its periphery which is partially closed by an endless belt supported by the casting wheel and an idler pulley. The casting wheel and the endless belt cooperate to provide a mold into one end of which molten metal is poured to solidify and from the other end of which the cast bar is emitted in substantially that condition in which it is solidified.
The rolling mill is of conventional type having a plurality of roll stands arranged to hot-form the cast bar by a series of deformations. The continuous casting machine and the rolling mill are positioned relative to each other so that the cast bar enters the rolling mill substantially immediately after solidification and in substantially that condition in which it solidified. In this condition, the cast bar is at a hot-forming temperature within the range of temperatures for hot-forming the cast bar at the initiation of hot-forming without heating between the casting machine and the rolling mill. In the event that it is desired to closely control the hot-forming temperature of the cast bar within the conventional range of hot-forming temperatures, means for adjusting the temperature of the cast bar may be placed between the continuous casting machine and the rolling mill without departing from the inventive concept disclosed herein.
The roll stands each include a plurality of rolls which engage the cast bar. The rolls of each roll stand may be two or more in number and arranged diametrically opposite from one another or arranged at equally spaced positions about the axis of movement of the cast bar through the rolling mill. The rolls of each roll stand of the rolling mill are rotated at a predetermined speed by a power means such as one or more electric motors and the casting wheel is rotated at a speed generally determined by its operating characteristics. The rolling mill serves to hot-form the cast bar into a rod of a cross-sectional area substantially less than that of the cast bar as it enters the rolling mill.
The peripheral surfaces of the rolls of adjacent roll stands in the rolling mill change in configuration; that is, the cast bar is engaged by the rolls of successive roll stands with surfaces of varying configuration, and from different directions. This varying surface engagement of the cast bar in the roll stands function to knead or shape the metal in the cast bar in such a manner that it is worked at each roll stand and also to simultaneously reduce and change the cross-sectional area of the cast bar into that of the rod.
As each roll stand engages the cast bar, it is desirable that the cast bar be received with sufficient volume per unit of time at the roll stand for the cast bar to generally fill the space defined by the rolls of the roll stand so that the rolls will be effective to work the metal in the cast bar. However, it is also desirable that the space defined by the rolls of each roll stand not be overfilled so that the cast bar will not be forced into the gaps between the rolls. Thus, it is desirable that the rod be fed toward each roll stand at a volume per unit of time which is sufficient to fill, but not overfill, the space defined by the rolls of the roll stand.
As the cast bar is received from the continuous casting machine, it usually has one large flat surface corresponding to the surface of the endless band and inwardly tapered side surfaces corresponding to the shape of the groove in the casting wheel. As the cast bar is compressed by the rolls of the roll stands, the cast bar is deformed so that it generally takes the cross-sectional shape defined by the adjacent peripheries of the rolls of each roll stand.
Thus, it will be understood that with this apparatus, cast aluminum alloy rod of an infinite number of different lengths is prepared by simultaneous casting of the molten aluminum alloy and hot-forming or rolling the cast-aluminum bar.
According to the method described in the aforementioned copending application, the continuous rod was cold-drawn through a series of progressively constricted dies, without intermediate anneals, to form a continuous wire of desired diameter. Thereafter, the wire was annealed or partially annealed to obtain a desired tensile strength and cooled. The annealing operation was disclosed as being continuous as in resistance annealing, induction annealing, convection annealing by continuous furnaces or radiation annealing by continuous furnaces, or, preferably, batch annealed in a batch furnace.
In order to produce a product having improved percent ultimate elongation, increased ductuity and fatigue resistance, and increased electrical conductivity in accordance with the objects of the aforementioned copending application, it was necessary to anneal at temperatures of about 450.degree. F to about 1200.degree. F when continuously annealing with annealing times of about 5 minutes to about 1/10,000 of a minute. On the other hand, when batch annealing, a temperature of approximately 400.degree. F to about 750.degree. F was employed with resident times of about 30 minutes to about 24 hours.
It was further disclosed in the aforementioned copending application that the aluminum base alloy after cold-working includes an intermetallic compound precipitate. The compound is identified as Cobalt aluminate (Co.sub.2 Al.sub.9). This intermetallic compound is found to be very stable and especially so at high temperatures. The compound also has a low tendency to coalesce during annealing of products formed from the alloy and the compound is generally incoherent with the aluminum matrix. The mechanism of strengthening for this alloy is in part due to the dispersion of the intermetallic compound as a precipitate throughout the aluminum matrix. The precipitate tends to pin dislocation sites which are created during cold working of products formed from the alloy. Upon examination of the intermetallic compound precipitate in a cold drawn product, it is found that the precipitates are oriented in the direction of drawing. In addition, it is found, when examining a No. 10 gauge wire, that the precipitates are rod-like in configuration and a majority are 1/4 to 1/2 microns long and about 1/8 micron in diameter. The precipitates may also be spherical or plate-like. The cell size in this tested sample of wire is approximately 1/2 to 1 micron in cross-section.
Other intermetallic compounds may also be formed depending upon the constituents of the melt and the relative concentrations of the alloying elements. Those intermetallic compounds include the following: NiAl.sub.3, Ni.sub.2 Al.sub.3, MgCoAl, FeAl.sub.3, Fe.sub.2 Al.sub.5, Co.sub.4 Al.sub.13, CeAl.sub.4, CeAl.sub.2, VAl.sub.11, VAl.sub.7, VAl.sub.6, VAl.sub.3, WAl.sub.12, Zr.sub.3 Al, Zr.sub.2 Al, LaAl.sub.4, LaAl.sub.2.